Personally, I think both need a zoo. When it comes down to which I think needs it more, I have to go with Vegas, for multiple reasons. For starters, Austin is only an hour away from San Antonio. However, the biggest reason I believe Vegas does is because there is nothing to do there for the local population. At least that is what I have been told by a friend that grew up there. He said the only thing to do is really the strip and other casinos or it is at least all at casinos. In terms of family oriented things to do, dragging your kids to the Aquarium on the Vegas strip probably isn't high on your priority list. He said the people there also don't won't to deal with the crowds that are on the strip either. Obviously any attraction, whether local or for tourists, will attract crowds, but going to the strip to just go to the Aquarium is extra hectic because your dealing with a huge crowd just walking on the streets. Other general comment about Austin, so there is no room in the city, which I get it happens, but why can't it be in a surrounding suburb where there is more land? Why does it specifically have to be in Austin versus just the metro area to make it work? I ask because I'm from Minnesota, and no Minneapolis does not have a zoo within its boundaries, but I wouldn't say it doesn't have a zoo because the Minnesota Zoo is only 30 minutes away. I guess I understand this question more as which area needs it more versus which city specifically.
Some would, but I doubt most or many would. People just do not go to Vegas to see a zoo, and without a rental car it would not be super easy to get to. Sure Uber and taxi would work, but taxi's are not prevalent off of the strip or DT. It is tough to get many people outside in the daytime in the summer months too....I love Vegas, it is my favorite travel destination - but I think the zoo would need to be for residents mostly, which is actually a good thing. Vegas has little to do for a resident, with kids especially so.
I would and have left the Strip for a variety of reasons (scrapbook store, Harley dealership) and have been to the joke that was the Southern Nevada Zoological Park, which was off-strip. I have yet to visit the Lion Habitat Ranch in Henderson. As for animals and the extreme summer temperatures, if they take a page from the Phoenix Zoo book, they would only keep animals that can handle hot weather.
I think that many or most of the forum members would visit a zoo in LV. But we are not exactly the typical Vegas tourist or even animal enthusiast, we are zoo enthusiasts and a rather fringe group. As I said though, if the zoo were designed for residents in mind I think it could be very successful.